1. Field of the Invention
The present invention relates to a magnetron plasma process apparatus for use in manufacturing semiconductor devices or the like.
2. Description of the Related Art
Hitherto known as magnetron plasma process apparatuses are, for example, a dry etching apparatus and a thin-film forming apparatus. In a magnetron plasma process apparatus of this type, magnetron plasma is generated in the reaction chamber, and the radicals, electrons, ions, or the like existing in the plasma are utilized to achieve a desired process such as etching or forming of a thin film.
A magnetron plasma etching apparatus, one type of such a magnetron plasma process apparatus, will be described. As is shown in FIG. 1, the etching apparatus has a process chamber 2, i.e., a reaction chamber. The chamber 2 has an inlet port and an outlet port. Etching gas can be introduced into the chamber 2 via the inlet port and can be exhausted from the chamber 2 through the outlet port. A lower electrode 4 is located within the chamber 2. Placed on this electrode 4 is a semi-conductor wafer 3 which is the object to be processed with plasma. The lower electrode 4 is electrically connected to a high-frequency power supply 5 which is located outside the process chamber 2. The top wall of the process chamber 2 functions as upper electrode 6, which is connected to the ground. The lower electrode 4 and the upper electrode 6 form a pair of parallel flat electrodes.
In operation, etching gas is introduced into the process chamber 2 via the inlet port, and the high-frequency power supply 5 supplies a high-frequency power of 380 KHz or 13.56 MHz between the electrodes 4 and 6. Plasma of the etching gas is thereby generated in the space between the electrodes 4 and 6, by means of cathode coupling (RIE). The ions or radicals in the plasma react with the silicon compound in the wafer 3, thereby etching the semiconductor wafer 3.
Permanent magnets 7 are located above the process chamber 2. These magnets 7 are secured to a support 8, which is connected to a shaft 9. The shaft 9 is rotated by an electric motor (not shown), thereby rotating the permanent magnets 7 around the axis of the shaft 9. As a result, a magnetic field indicated by the broken lines in FIG. 1 is generated between the lower electrode 4 and the upper electrode 6. The horizontal component of this magnetic field extends at right angles to the electric field generated between the electrodes 4 and 6, composing a closed electromagnetic field. Due to the closed electromagnetic field, electrons assume cycloidal motion. Hence, the electrons colloid with the molecules of the etching gas at elevated frequency, generating more and more plasma. This increases the etching speed of the wafer 3.
The conventional plasma etching apparatus, described above, has drawbacks, however.
The magnetic field the magnets 7 apply has not only a horizontal component but also a considerably prominent vertical component, as can be understood from FIG. 1. The magnitude of this vertical component differs in accordance with the position in the surface of the semi-conductor wafer 3. Therefore, the self bias (V.sub.DC) applied on a portion of the wafer 3 is different from the self bias applied on another portion thereof. Any portion of the wafer 3 that is applied with an excessive self will be charged excessively. The gate oxide film formed on this portion of the wafer 3 is broken in some cases.
Further, since in the conventional plasma etching apparatus the magnets are provided above the chamber 2, the magnetic field generated by the magnets 7 may leak to the components other than the process chamber 2, such as sensors each having a permanent magnet, inevitably causing malfunction of the sensors. If an apparatus in which electron beams are used is arranged besides the magnetron etching apparatus, it will be adversely influenced by the leakage magnetic field leaking from the plasma etching apparatus.
These drawbacks are inherent in not only a magnetron plasma etching apparatus, but also in a plasma sputtering apparatus and a plasma CVD apparatus, which uses magnetron plasma.